1. Field of the Invention
The present invention relates to a conversion circuit for converting differential signal into single-phase signal. More specifically, the present invention relates to a conversion circuit for converting differential signal into single-phase signal, which has a reduced chip area and improved power efficiency.
2. Description of the Related Art
In the prior art, there is a conversion circuit which convert differential signal with different phase into single-phase signal. For example, the conversion circuit is used in portable telephones, wireless LANs, and other applications in which, after conversion, the single-phase signal is output to a single antenna to perform communication.
As the conversion circuits of the prior art, for example a circuit which uses transformer 101 (or Balun), which is passive element (see FIG. 8A), and a circuit which uses transistors 104, 105 (see FIG. 8B), are widely used. In either case, differential signals are input from two input terminals IN and INX, and single-phase signal is output from an output terminal OUT.
Further, a conversion circuit for converting differential signal into single-ended signal, have also been disclosed which combine a plurality of current mirror circuits configured from transistors, so as to obtain single-ended signals without distortion (see for example the Japanese Patent Laid-open No. 8-288762).
However, in the case of the conversion circuit employing a transformer shown in FIG. 8A, the chip area is increased by the amount of the transformer 101. And in the case of the conversion circuit employing transistors shown in FIG. 8B, the single-phase signal OUT is obtained using only the output side of the inverted signals INX of the input differential signals, so that power loss is considerable.
Further, because in the above Patent Reference 1 a plurality of current mirror circuits are combined, the number of components is large, and the chip area similarly is increased.